A balun is used to match between a single-ended (or unbalanced) signal and a pair of differential (or balanced) signals.
Typically, a conventional RF balun is in the form of a magnetic core wound with windings. Such RF balun has a wide working frequency band of up to a GHz-level. Referring to FIG. 1, a curve 91 illustrates partially an insertion loss measurement result of such conventional RF balun within a frequency range of from 450 MHz to 790 MHz. From the curve 91 of FIG. 1, such conventional RF balun has an insertion loss less than −6 dB such that it is suitable for RF signals within an UHF band of from 470 MHz to 770 MHz, for example, a terrestrial digital television frequency band. However, such conventional RF balun requires expensive fabrication materials, and involves a process for soldering the magnetic core onto a printed circuit board (PCB), thereby resulting in a high fabrication cost.
Referring to FIG. 2, another conventional balun on a PCB 19 is shown to include a ground pattern 16 and a signal pattern 15 that are directly formed on the PCB 19, which is a less expensive approach. Referring again to FIG. 1, a curve 92 illustrates partially an insertion loss measurement result of the conventional balun of FIG. 2 within the frequency range of from 450 MHz to 790 MHz. From the curve 92 of FIG. 1, it is noted that this conventional balun may merely support RF signals within the limited working frequency range of from 500 MHz to 600 MHz, roughly. Thus, this conventional balun with relatively narrow bandwidth is not suitable for terrestrial digital television signals in the UHF band.